Thought you would be interested in the following link, from the blog of Mike Jones of Microsoft.
Topic:
There's now an OAuth working group draft of the OAuth 2.0 Token Exchange specification, which provides Act-As and On-Behalf-Of functionality for OAuth 2.0. This functionality is deliberately modelled on the same functionality present in WS-Trust.
Link:
http://self-issued.info/?p=1276
Alan
